The maintenance of aircraft often involves the performance of maintenance activities within a confined work space within the aircraft. Such activities can include the inspection of aircraft parts and structures, along with the replacement and repair of parts. Such maintenance is often required as a consequence of airworthiness directives issued by the Federal Aviation Administration (FAA), which specify detailed and exacting standards to which aircraft maintenance is to be performed.
A non-limiting example of such an airworthiness directive is AD 2001-02-09 which requires a lower chord tang/bolt hole inspection on Boeing 757 aircraft at a specified frequency of Total Ship Cycles (TSC) over the life of the aircraft. The lower chord on an aircraft is the structure which helps to transfer the operational loads of the engine and secure the engine via the pylori strut to the wing of the aircraft. The lower chord is located within the pylori between the engine and the wing, with a series of bolts inserted through these structures securing them together. This inspection is required at specified intervals to assess the structural integrity of the lower chord and the ability of the chord assembly to sustain the operational load of the engine pylori. The assessment of the integrity of the bolt holes in the lower chord is therefore an integral part of the required inspection.
Should the inspection of the lower chord reveal crack indications in the lower chord bolt holes, installation of a new midchord configuration and possible replacement of the lower chord may be necessary. Installation of the new midchord configuration of the lower chord, if required, is a costly and time-consuming process, resulting in a typical out of service time for an aircraft of at least 30 days at a cost often exceeding $200,000. However, if crack indications are limited and are found to exist within certain limits specified in the airworthiness directive, oversizing of the bolt hole to remove the crack, rather than installation of the new midchord, may be possible. Cracks which are not addressed, through either oversizing until removal or a repair, can continue to increase in length and can make replacement of the lower chord necessary.
The required initial inspection requires an insurance cut which consists of the reaming or oversizing of the lower chord bolt holes to increase the diameter of the holes. This oversizing is performed in increments until the cracks, or fatigued material, are removed. This oversizing, through removal of the fatigued material and installation of larger bolts in the lower chord bolt holes, will give the lower chord/pylori structure the necessary strength for continued operations, and defer the need for installation of a new midchord configuration specified under the airworthiness directive.
It can be seen, therefore, that the accomplishment of the oversizing repair on the lower chord can prevent cracks which would otherwise require premature installation of the new midchord configuration and possible lower chord replacement. This oversizing repair thus shortens the time an aircraft would need to be out of service and reduces the total maintenance costs related to this airworthiness directive.
In order to accomplish such a repair, an apparatus and method for the accurate reaming of the lower chord bolt holes is required. Such a repair is difficult given the thickness of the chord assembly, which consists of three metal surfaces positioned back-to-back, each approximately ¼ of an inch thick, thereby requiring drilling through a steel work surface approximately ¾ of an inch in total thickness. Attempts to effectuate such reaming “free-hand”, without the use of a guide, would typically lead to inaccurate, misaligned reamings, resulting in damage to the lower chord structure.
The difficulty of performing the oversizing noted above is increased as well whenever limited working space is presented and within which the operation must be accomplished. In the instance of the above oversizing operation, the lower chord is typically accessed through a small access panel on the aircraft strut assembly, with the access panel often measuring no more than one square foot. Once accessed, the working space around the lower chord itself is likewise limited. It is difficult for the person performing this repair, as well as other positionally critical drilling operations, to be able to perform an accurate reaming, particularly so that the oversizing is performed within the required tolerances and aligned with the bolt holes, within such a confined work space. If not performed properly, the reaming can result in damage to the lower chord, necessitating premature installation of the new midchord configuration, thereby resulting in increased out of service time and maintenance costs which the oversizing was intended to prevent.
Therefore, there is a need for a tool and method to provide a precise, highly accurate reaming of a work surface in a confined work space.